A conventional welding torch 10 illustrated in FIG. 1 generally includes a cable assembly connected to a torch body including a handle 11, a neck such as a gooseneck 12 extending from the handle, and a torch head at a distal end of the gooseneck. The torch head typically includes a retaining head and/or diffuser 13, a contact tip 14, and a nozzle 15. Welding wire (consumable electrode) and shielding gas are fed through the cable assembly and gooseneck to the torch head, where the welding wire and shielding gas are fed out of the contact tip and nozzle.
Common metal welding techniques employ heat generated by electrical arcing to transition a portion of a workpiece to a molten state and to add filler metal from the welding wire. Energy (e.g., welding current) is transferred from the cable assembly and gooseneck through the front components of the torch including the retaining head and contact tip, to the consumable electrode welding wire. When a trigger on the welding torch is operated (or an “on” signal is assigned by a robot/automatic controller in the case that the torch is used in a robotic system), electrode wire is advanced toward the contact tip, at which point current is conducted from the contact tip into the exiting welding wire. A current arc forms between the electrode wire and the workpiece, completing a circuit and generating sufficient heat to melt the electrode wire to weld the workpiece. The shielding gas helps generate the arc and protects the weld. As the electrode wire is consumed and becomes a part of the weld, new electrode wire is advanced, continuously replacing the consumed electrode wire and maintaining the welding arc.
In order to increase welding speeds (e.g., the travelling speed) and to reduce spatter generation in welding applications, welding power sources have recently been utilizing modern waveforms that are represented by pulse and controlled short circuit. These waveforms typically use high peak current (I_Peak) in a short pulse period and high current ramp rate.
The high welding current and high current ramp rate transferring across the contact tip—electrode wire interface during pulse welding applications causes local melt or evaporation (e.g., arc erosion) on both the electrode wire and the contact tip. For example, burn marks form on the electrode wire as it is fed through the contact tip. This pattern of burn marks on the electrode wire is a characteristic feature of modern pulse waveform welding and is not seen on electrode wire fed through contact tips during constant voltage welding modes. Arc erosion during pulse welding applications causes substantial wear removal of the contact tip, and practical data indicates that contact tips deteriorate faster in pulse welding applications in comparison to constant voltage applications.
As a contact tip is used and deteriorated, the energy transfer efficiency between the contact tip and the electrode wire decreases. This results in lower energy consumption at the arc. When the energy consumption is too low to maintain a smooth welding arc, stubbing occurs, which causes undesired welding defects such as cold welding and discontinuous beads.
One method that has been used to reduce arc erosion in pulse welding applications is to increase the mechanical contact force between the contact tip and the electrode wire. The electrical resistance at the contact point decreases as the contact force increases. Thus, less heat is generated and consumed at the contact tip—electrode wire interface, and there is less chance of arc erosion such as micro-sparkling, local melting, and local evaporation. Various contact tip and welding torch designs have been proposed to improve the mechanical contact between the contact tip and electrode wire. However, these designs are either too expensive to be commercialized, or too fragile to tolerate the harsh nature of the welding environment, such as spatter.